1. Field of the Invention
The present invention relates to an image reading apparatus. The present application is based on Japanese Patent Application No. Hei. 11-334557, which is incorporated herein by reference.
2. Description of the Related Art
A flatbed image reading apparatus has hitherto been known as an example of an image reading apparatus for reading an original, such as a graphic image or characters. An image reading table comprised of a transparent plate, such as glass, is provided on the upper surface of a box-shaped housing of the flatbed image reading apparatus. A carriage is disposed within the housing and is moved parallel to the image reading table by a driving device. The carriage is equipped with a light source and a line sensor comprised of a row of photoelectric transducers. Light originating from the light source of the carriage is reflected by the surface of an original located on the image reading table, and a condenser lens converges the light on the line sensor.
The thus-converged light is converted into an electric signal by the line sensor. The electric signal is further converted into a digital signal by a converter. After having been subjected to correction, such as shading correction, in an image processing section of the image reading apparatus, the digital signal is output to an external personal computer as image data.
When a user plugs a power cord to an outlet and turns on a light source switch, the light source is illuminated. The image reading apparatus performs a warm-up operation until the amount of light originating from the light source becomes sufficient for reading an original. After having completed the warm-up operation, the image reading apparatus enters a standby state in which it can read an original. The time required for performing a warm-up operation may vary according to the type of a light source. For example, a xenon lamp employed for a higher-end model requires a warm-up time of 0.1 sec. or less, and a mercury lamp employed for a prevailing model requires a warm-up time of one min. or thereabouts.
The U.S. Environmental Protection Agency (EPA) has issued recommendations concerning energy conservation; that is, the so-called Energy Star program for reducing power consumed while a device remains inoperative. Computer peripheral devices which are not limited to image reading apparatuses and are to comply with the Energy Star program must be controlled such that the devices enter a power economizing state in which power consumed within the devices falls below a predetermined value.
When the image reading apparatus is controlled to so as to remain in an energy economizing state, internal power consumed by the image reading apparatus is preferably minimized. To this end, a reduction in power consumption must be implemented not only in the light source but also in every circuit of the image reading apparatus, such as an optical sensor or an image processing section having a storage section provided therein.
In the event of an interruption in power supplied to the storage section of the image processing section storing data which needs not be updated within a short period of time, such as a gamma function to be used for preparing image data, data stored in the storage section, such as a gamma function, are also deleted. If the data stored in the storage section are deleted, the image reading apparatus returns to a standby state. When power supply is resumed, there arises a necessity for reacquiring the data. Every time the image reading apparatus shifts to a standby state from the power economizing state and the optical sensor and the transducer are initialized, the characteristic values unique to the optical sensor and the transducers must be recaptured. As a result, a warm-up operation during which the image reading apparatus shifts from the power economizing state to the standby state requires much time or involves re-set-up of the image reading apparatus, thereby resulting in a decrease in operability of the image reading apparatus.
Even when power supplied to an image pick-up section and an image processing section is stopped, an electric current flows through some circuits, such as a circuit for oscillating a clock signal. A signal current which is to originally flow from a transducer provided in the image pick-up section to the processing section may flow from the processing section to the transducer, thereby breaking elements included in the transducer.
It is an object of the present invention to provide an image reading apparatus which can reduce power consumption and prevent breakage of elements. Further, it is another object of the present invention to provide an image reading apparatus capable of improving operability.
To achieve the above objects, according to the present invention, there is provided an image reading apparatus which comprises an image reading table on which an original is placed, a light source which illuminates the original, an image pickup section including an optical sensor which converts, into an electric signal, at least one of a light reflected from the original and a light having been transmitted through the original, and a converter which converts the electric signal into a digital signal, an image processing section which produces image data on the basis of the digital signal and can output the image data, a control section capable of controlling the light source, the image pickup section, and the image processing section so as to enter one of an operating state in which the original is read, a standby condition in which the image reading apparatus is in a standby condition while remaining able to read the original, and a power economizing state in which power to be consumed is reduced, a first switching device which connects or disconnects supply of power to the image pickup section, and a second switching device which establishes or cancels an electrical connection between the converter and the image processing section. Further, according to the present invention, it is preferable that when the standby condition is shifted to the power economizing state, the control section causes the first switching device to electrically open after having electrically opened the second switching device. Furthermore, according to the present invention, it is preferable that when the power economizing state is shifted to the standby condition, the control section causes the second switching device to electrically close after having electrically closed the first switching device.
The second switching device cancels an electrical connection between the transducer and the image processing section, thereby preventing flow of a signal from the image processing section to the transducer. Flow of an electric current from the image processing section to the transducer can be interrupted by switching the first and second switching devices at different timings. The image reading apparatus can reduce power consumption by a greater amount than does a related image reading apparatus which reduces power consumption by extinguishing the light source, thereby preventing breakage of elements.
In the image reading apparatus according to the present invention, it is preferable that the image processing section is electrically energized in the power economizing state. Thus, it is preferable that an electric current flows through the image processing section even when the image reading apparatus is in the power economizing state. Data which are preferably preserved for a long period of time, such as a gamma function, can be stored by permitting flow, to the image processing section, of a minimum electric current required for presenting data, thereby obviating a necessity for recapturing data when the image reading apparatus shifts from the power economizing state to the standby state. Therefore, the image reading apparatus can be warmed up within a short period of time, thereby obviating re-setup of the image reading apparatus and improving operability of the same.
In the image reading apparatus according to the present invention, it is preferable to be further comprised of a ventilating section capable of blowing air to the light source section, the image pick-up section, the image processing section, and a control section of the image reading apparatus, wherein the ventilating section operates in association with operation of the image pickup section. Accordingly, a circuit which produces a large amount of heat, such as a light source, can be cooled. The ventilating section operates in association with operation of the image pick-up section. When the light source is extinguished in a power economizing state and when the supply of power to the image pick-up section is stopped, the ventilating section is inoperative. Consequently, even in a case where the image reading apparatus is equipped with the ventilating section, power consumption of the image reading apparatus can be reduced.
In the image reading apparatus according to the present invention, it is preferable that the control section captures information on the image pickup section in the standby condition, and the control section initializes the image pickup section on the basis of the information when the power economizing state is shifted to the standby condition. For example, when the image reading apparatus remains in a standby state, the control section captures information about the image pick-up section, such as a photoelectric-transducing characteristic of an optical sensor or an offset or gain of the transducer. When the image reading apparatus shifts from a power economizing state to a standby state, the image pick-up section is initialized on the basis of the thus-captured information, thus obviating a necessity for resetting of the information about the image pick-up section when the image reading apparatus shifts to a standby state. The image pick-up section can be initialized within a short period of time, thus improving the operability of the image reading apparatus.
In the image reading apparatus according to the present invention, it is preferable to be further comprised of an instruction input section which enables entry, with respect to the control section from an outside, of an instruction for instructing to shift from the power economizing state to the standby condition. Accordingly, the image reading apparatus can be shifted from the power economizing state to the standby state, by the user merely entering an instruction to the instruction input section, thereby facilitating handling of the image reading apparatus and improving the operability of the same.